The present invention relates to a ring-like hydraulic dynamic bearing having axial dynamic pressure portions and a radial dynamic pressure portion contiguous to each other and to a spindle motor using the hydraulic dynamic bearing.
As a bearing for a spindle motor for a hard disk device, there is used a hydraulic dynamic bearing having a shaft portion and a bearing portion for supporting the bearing portion. The hydraulic dynamic bearing is formed with dynamic pressure generating grooves at either one of opposed faces of the shaft and bearing portions and is formed with a layer of a lubricant at high pressure in a very small clearance disposed between the shaft and bearing portions so that during rotation of the shaft portion noncontact rotation of the shaft portion is realized.
FIG. 8 is a sectional view showing a conventional ring-like hydraulic dynamic bearing. A ring-like hydraulic dynamic bearing 100 is provided with a shaft portion 103 constituted by fixing a ring 102 to an end portion 101A of a shaft main body 101 by press fitting and a bearing portion 104 supporting the shaft portion 103 and is constituted such that the ring 102 at the shaft portion 103 rotatably contained in a recess portion 105A of a main body 105 of the bearing portion 104 is prevented from coming out from the recess portion 105A by a circular disk-like thrust holding member 106.
An upper face 102A and a lower face 102B of the ring 102 are respectively formed with axial dynamic pressure generating grooves G1 and G2 and a peripheral face 102C of the ring 102 is formed with radial dynamic pressure generating grooves G3.
A lubricant for generating dynamic pressure is held between the shaft portion 103 and the bearing portion 104 and accordingly, when the shaft portion 103 is rotated, axial dynamic pressure is generated between the upper face 102A and the circular disk-like thrust holding member 106 by the axial dynamic pressure generating grooves G1 and axial dynamic pressure is generated between the lower face 102B and a bottom face of the recess portion 105A by the axial dynamic pressure generating grooves G2. Further, radial dynamic pressure is generated between the peripheral face 102C and an inner peripheral face of the recess portion 105A by the radial dynamic pressure generating grooves G3. As a result, axial dynamic pressure bearings and a radial dynamic pressure bearing which are lubricant layers at high pressure are formed between the shaft portion 103 and the bearing portion 104 to thereby enable to rotate the shaft portion 103 by noncontact rotation.
As described above, according to the conventional ring-like radial dynamic bearing, there is constructed the constitution in which the radial dynamic pressure generating face and the axial dynamic pressure generating faces are contiguous to each other and accordingly, the following problem is posed. That is, when the shaft portion 103 is rotated, by the axial dynamic pressure generating grooves G1, the axial dynamic pressure generating grooves G2 and the radial dynamic pressure generating grooves G3 which are respectively formed at the upper face 102A, the lower face 102B and the peripheral face 102C of the ring 102, the lubricant is drawn to central portions of the respective dynamic pressure generating faces and negative pressure is produced at portions of the upper face 102A and the peripheral face 102C contiguous to each other and portions of the lower face 102B and the peripheral face 102C contiguous to each other. As a result of producing the negative pressure caused by mutual interference, air bubbles are liable to produce at the portions of the dynamic pressure generating faces contiguous to each other which hamper flow of the lubricant and accordingly, there causes a drawback in which sufficient dynamic pressure is not generated and the bearing rigidity is deteriorated.